Heroin-assisted treatment is a therapeutic option that has been added to the range of opioid substitution treatment (OST) in a growing number of countries in the past two decades, as its evidence base has grown more extensive and secure. It involves the provision of diamorphine to patients, usually those who have not gained benefit from more traditional OST employing methadone, etc. Diamorphine doses are given under clinical supervision in a safe and clean medical setting and the medication elements are combined with intensive psychosocial support mechanisms. HAT is currently provided with positive outcomes in several countries, including Switzerland, Germany, the UK, Denmark, Spain, Canada and the Netherlands.